KR102460499B1 - shovel - Google Patents

Abstract

A shovel according to an embodiment of the present invention includes a lower traveling body (1), an upper revolving body (3) mounted rotatably on the lower traveling body (1), and a main pump (3) mounted on the upper revolving body (3) 14), a hydraulic actuator driven by hydraulic oil discharged from the main pump 14, and a bleed valve that controls the flow rate of hydraulic oil flowing into the hydraulic oil tank without passing through the hydraulic actuator among the hydraulic oil discharged by the main pump 14 (177) and a controller (30) for controlling the opening area of the bleed valve (177) according to the magnitude of pulsation in the pressure of the hydraulic oil supplied from the main pump (14) to the hydraulic actuator.

Description

shovel

The present disclosure relates to a shovel having a hydraulic actuator driven by hydraulic oil discharged by a hydraulic pump.

Conventionally, a shovel capable of controlling the bleed-off of a directional selector valve corresponding to each of a plurality of hydraulic actuators sharing a main pump with one cut valve is known (see Patent Document 1).

This shovel is designed to suppress the turning acceleration of the upper revolving body when the working radius of the working attachment is small by increasing the bleed-off in accordance with the reduction of the working radius of the working attachment.

Patent Document 1: Japanese Patent Application Laid-Open No. 10-18359

However, the above-described shovel only controls the bleed-off with the cut valve in order to stabilize the turning maneuverability, and does not use the cut valve to suppress the pulsation of the pressure of the hydraulic oil in the hydraulic circuit. Therefore, the pulsation of the pressure of the hydraulic oil in the hydraulic circuit cannot be suppressed.

In view of the above, it is desirable to provide a shovel capable of suppressing the pulsation of the pressure of the hydraulic oil in the hydraulic circuit.

A shovel according to an embodiment of the present invention includes a lower traveling body, an upper revolving body mounted rotatably on the lower traveling body, a hydraulic pump mounted on the upper revolving body, and hydraulic oil discharged by the hydraulic pump. A hydraulic actuator driven, a bleed valve for controlling the flow rate of hydraulic oil flowing in the hydraulic oil tank without passing through the hydraulic actuator among the hydraulic oil discharged by the hydraulic pump; and a control device for controlling the opening area of the bleed valve in accordance with the magnitude of the pulsation in the bleed valve.

By the means described above, it is possible to provide a shovel capable of suppressing the pulsation of the pressure of the hydraulic oil in the hydraulic circuit.

BRIEF DESCRIPTION OF THE DRAWINGS It is a side view of the shovel which concerns on embodiment of this invention.
Fig. 2 is a block diagram showing a configuration example of the drive system of the shovel of Fig. 1;
Fig. 3 is a schematic diagram showing a configuration example of a hydraulic circuit mounted on the shovel of Fig. 1;
4 is a flowchart of an example of a bleed flow rate increase/decrease process.
Fig. 5 shows the temporal transition of the pump discharge pressure and the proportional valve characteristic when the bleed flow rate increase/decrease process is executed during the boom raising operation.
6 is a flowchart of another example of the bleed flow rate increase/decrease process.
Fig. 7 is a schematic diagram showing another configuration example of a hydraulic circuit mounted on the shovel of Fig. 1;

1 is a side view of a shovel (excavator) according to an embodiment of the present invention. On the lower traveling body 1 of the shovel, the upper revolving body 3 is mounted so as to be able to turn through the revolving mechanism 2 . The boom 4 is mounted on the upper swing body 3 . An arm 5 is attached to the tip of the boom 4 , and a bucket 6 as an end attachment is attached to the tip of the arm 5 .

The boom 4, the arm 5, and the bucket 6 constitute an excavation attachment as an example of the attachment, and are hydraulically driven by the boom cylinder 7, the arm cylinder 8, and the bucket cylinder 9, respectively. A boom angle sensor (S1) is mounted on the boom (4), an arm angle sensor (S2) is mounted on the arm (5), and a bucket angle sensor (S3) is mounted on the bucket (6).

The boom angle sensor S1 detects a rotation angle of the boom 4 . In this embodiment, the boom angle sensor S1 is an acceleration sensor, and can detect the rotation angle of the boom 4 with respect to the upper swing body 3 (hereinafter referred to as "boom angle α"). The boom angle α becomes 0 degrees when, for example, the boom 4 is most lowered, and increases as the boom 4 is raised.

The arm angle sensor S2 detects the rotation angle of the arm 5 . In the present embodiment, the arm angle sensor S2 is an acceleration sensor, and can detect the rotation angle of the arm 5 with respect to the boom 4 (hereinafter referred to as "dark angle β"). The arm angle beta becomes 0 degrees when the arm 5 is most closed, for example, and becomes large as the arm 5 is opened.

The bucket angle sensor S3 detects the rotation angle of the bucket 6 . In this embodiment, the bucket angle sensor S3 is an acceleration sensor, and can detect the rotation angle of the bucket 6 with respect to the arm 5 (hereinafter referred to as "bucket angle γ"). The bucket angle γ is, for example, 0 degrees when the bucket 6 is most closed, and increases as the bucket 6 is opened.

The boom angle sensor (S1), the arm angle sensor (S2), and the bucket angle sensor (S3) are, respectively, a potentiometer using a variable resistor, a stroke sensor for detecting the stroke amount of the corresponding hydraulic cylinder, and rotation around the connecting pin It may be a rotary encoder that detects an angle, a gyro sensor, a combination of an acceleration sensor and a gyro sensor, or the like.

The boom cylinder 7 is equipped with a boom rod pressure sensor S7R and a boom bottom pressure sensor S7B. The arm cylinder 8 is equipped with an arm rod pressure sensor S8R and an arm bottom pressure sensor S8B. The bucket cylinder 9 is equipped with a bucket load pressure sensor S9R and a bucket bottom pressure sensor S9B.

The boom rod pressure sensor S7R detects the pressure of the oil chamber on the rod side of the boom cylinder 7 (hereinafter referred to as "boom rod pressure"), and the boom bottom pressure sensor S7B is the bottom of the boom cylinder 7 . The pressure of the side oil chamber (hereinafter referred to as "boom bottom pressure") is detected. The arm rod pressure sensor S8R detects the pressure of the oil chamber on the rod side of the arm cylinder 8 (hereinafter referred to as "arm rod pressure"), and the arm bottom pressure sensor S8B is the bottom of the arm cylinder 8 . The pressure of the side oil chamber (hereinafter referred to as "arm bottom pressure") is detected. The bucket load pressure sensor S9R detects the pressure of the oil chamber on the rod side of the bucket cylinder 9 (hereinafter referred to as "bucket rod pressure"), and the bucket bottom pressure sensor S9B is the bottom of the bucket cylinder 9 . The pressure of the side oil chamber (hereinafter referred to as "bucket bottom pressure") is detected.

The upper revolving body 3 is provided with a cabin 10 serving as a cab, and a power source such as an engine 11 is mounted thereon. Further, the upper revolving body 3 is equipped with an aircraft inclination sensor S4, a revolving angular velocity sensor S5, and a camera S6.

The gas inclination sensor S4 detects the inclination of the upper revolving body 3 with respect to the horizontal plane. In the present embodiment, the aircraft inclination sensor S4 is an acceleration sensor that detects the inclination angles around the front and rear axes and the left and right axes of the upper revolving body 3 . The front-rear axis and the left and right axes of the upper revolving body 3 pass through the center point of the shovel, which is, for example, perpendicular to each other and is a point on the revolving axis of the shovel.

The turning angular velocity sensor S5 detects the turning angular velocity of the upper revolving body 3 . In this embodiment, it is a gyro sensor. It may be a resolver, a rotary encoder, or the like.

The camera S6 acquires an image of the periphery of the shovel. In the present embodiment, the camera S6 includes a front camera mounted on the upper revolving body 3 . The front camera is a stereo camera that images the front of the shovel, and is mounted on the roof of the cabin 10 , that is, outside the cabin 10 . You may attach to the ceiling of the cabin 10, ie, the inside of the cabin 10. The front camera can image the excavation attachment. The front camera may be a monocular camera.

A controller 30 is installed in the cabin 10 . The controller 30 functions as a main control unit that performs driving control of the shovel. In the present embodiment, the controller 30 is constituted by a computer including a CPU, a RAM, a ROM, and the like. Various functions of the controller 30 are realized by, for example, the CPU executing a program stored in the ROM.

Fig. 2 is a block diagram showing a configuration example of the drive system of the shovel of Fig. 1, in which a mechanical power transmission line, a hydraulic oil line, a pilot line, and an electric control line are indicated by double lines, thick solid lines, broken lines, and dotted lines, respectively.

The drive system of the shovel is mainly the engine 11, the regulator 13, the main pump 14, the pilot pump 15, the control valve 17, the operation device 26, the discharge pressure sensor 28, the operation pressure sensor. 29 , a controller 30 , and a proportional valve 31 .

The engine 11 is a drive source of the shovel. In this embodiment, the engine 11 is a diesel engine which operates so as to maintain a predetermined rotation speed, for example. In addition, the output shaft of the engine 11 is connected to the input shaft of the main pump 14 and the pilot pump 15 .

The main pump 14 supplies the hydraulic oil to the control valve 17 through the hydraulic oil line. In this embodiment, the main pump 14 is a swash plate type variable displacement hydraulic pump.

The regulator 13 controls the discharge amount of the main pump 14 . In the present embodiment, the regulator 13 controls the discharge amount of the main pump 14 by adjusting the swash plate inclination angle of the main pump 14 according to a control command from the controller 30 .

The pilot pump 15 supplies hydraulic oil to various hydraulic control devices including the operating device 26 and the proportional valve 31 through a pilot line. In this embodiment, the pilot pump 15 is a fixed displacement hydraulic pump.

The control valve 17 is a hydraulic control device that controls the hydraulic system in the shovel. The control valve 17 includes control valves 171 to 176 , and a bleed valve 177 . The control valve 17 may selectively supply hydraulic oil discharged by the main pump 14 to one or a plurality of hydraulic actuators through the control valves 171 to 176 . The control valves 171 to 176 control the flow rate of the hydraulic oil flowing from the main pump 14 to the hydraulic actuator, and the flow rate of the hydraulic oil flowing from the hydraulic actuator to the hydraulic oil tank. The hydraulic actuator includes a boom cylinder (7), an arm cylinder (8), a bucket cylinder (9), a hydraulic motor for left running (1A), a hydraulic motor for running on the right (1B), and a hydraulic motor for turning (2A). do. The bleed valve 177 controls the flow rate (hereinafter, referred to as "bleed flow rate") of the hydraulic oil discharged by the main pump 14 that flows into the hydraulic oil tank without passing through the hydraulic actuator. The bleed valve 177 may be provided outside the control valve 17 .

The operating device 26 is a device used by the operator to operate the hydraulic actuator. In this embodiment, the operating device 26 supplies the hydraulic oil discharged by the pilot pump 15 to the pilot port of the control valve corresponding to each of the hydraulic actuators via the pilot line. The pressure (pilot pressure) of the hydraulic oil supplied to each of the pilot ports is a pressure according to the operation direction and the amount of operation of the lever or pedal (not shown) of the operation device 26 corresponding to each of the hydraulic actuators.

The discharge pressure sensor 28 detects the discharge pressure of the main pump 14 . In the present embodiment, the discharge pressure sensor 28 outputs the detected value to the controller 30 .

The operation pressure sensor 29 detects the operation contents of the operator using the operation device 26 . In the present embodiment, the operation pressure sensor 29 detects the operation direction and operation amount of the lever or pedal of the operation device 26 corresponding to each of the hydraulic actuators in the form of pressure (operation pressure), and returns the detected value. output to the controller 30 . The operation contents of the operation device 26 may be detected using a sensor other than the operation pressure sensor.

The proportional valve 31 operates according to a control command output by the controller 30 . In this embodiment, the proportional valve 31 adjusts the secondary pressure introduced from the pilot pump 15 to the pilot port of the bleed valve 177 in the control valve 17 according to the current command output by the controller 30 . It is a solenoid valve that The proportional valve 31 operates so that the secondary pressure introduced into the pilot port of the bleed valve 177 increases as the current command increases, for example.

Next, with reference to FIG. 3, the structural example of the hydraulic circuit mounted on a shovel is demonstrated. Fig. 3 is a schematic diagram showing a configuration example of a hydraulic circuit mounted on the shovel of Fig. 1; In FIG. 3 , the mechanical power transmission line, the hydraulic oil line, the pilot line, and the electric control line are respectively indicated by double lines, thick solid lines, broken lines, and dotted lines, as in FIG. 2 .

The hydraulic circuit of FIG. 3 circulates hydraulic oil from the main pumps 14L and 14R driven by the engine 11 to the hydraulic oil tank via the pipelines 42L and 42R. The main pumps 14L and 14R correspond to the main pump 14 in FIG. 2 .

The pipe line 42L is a hydraulic oil line that connects each of the control valves 171 , 173 , 175L and 176L arranged in the control valve 17 in parallel between the main pump 14L and the hydraulic oil tank. The conduit 42R is a hydraulic oil line connecting each of the control valves 172 , 174 , 175R and 176R arranged in the control valve 17 in parallel between the main pump 14R and the hydraulic oil tank.

The control valve 171 supplies the hydraulic oil discharged by the main pump 14L to the hydraulic motor 1A for traveling on the left, and also discharging the hydraulic oil discharged by the hydraulic motor 1A for traveling on the left to the hydraulic oil tank. It is a spool valve that diverts the flow of

The control valve 172 supplies hydraulic oil discharged by the main pump 14R to the hydraulic motor 1B for right traveling, and also discharging the hydraulic oil discharged by the hydraulic motor 1B for right traveling to the hydraulic oil tank. It is a spool valve that diverts the flow of

The control valve 173 supplies the hydraulic oil discharged by the main pump 14L to the turning hydraulic motor 2A, and also discharges the hydraulic oil discharged by the turning hydraulic motor 2A to the hydraulic oil tank. It is a spool valve that switches the

The control valve 174 is a spool valve for supplying the hydraulic oil discharged by the main pump 14R to the bucket cylinder 9 and discharging the hydraulic oil in the bucket cylinder 9 to the hydraulic oil tank.

The control valves 175L and 175R supply the hydraulic oil discharged by the main pumps 14L and 14R to the boom cylinder 7, and also switch the flow of hydraulic oil to discharge the hydraulic oil in the boom cylinder 7 to the hydraulic oil tank. It's a spool valve.

The control valves 176L and 176R supply hydraulic oil discharged by the main pumps 14L and 14R to the female cylinder 8, and also switch the flow of hydraulic oil to discharge the hydraulic oil in the female cylinder 8 to the hydraulic oil tank. It's a spool valve.

The bleed valve 177L is a spool valve which controls the bleed flow rate with respect to the hydraulic oil discharged by the main pump 14L. The bleed valve 177R is a spool valve that controls the bleed flow rate with respect to the hydraulic oil discharged by the main pump 14R. The bleed valves 177L and 177R correspond to the bleed valve 177 of FIG. 2 .

The bleed valves 177L and 177R have, for example, a first valve position having a minimum opening area (degree of opening 0%) and a second valve position having a maximum opening area (degree of opening 100%). The bleed valves 177L and 177R can be moved steplessly between the first valve position and the second valve position.

The regulators 13L and 13R control the discharge amounts of the main pumps 14L and 14R by adjusting the swash plate inclination angle of the main pumps 14L and 14R. The regulators 13L and 13R correspond to the regulator 13 of FIG. 2 . The controller 30 adjusts the swash plate inclination angles of the main pumps 14L and 14R with the regulators 13L and 13R, for example, in accordance with an increase in the discharge pressures of the main pumps 14L and 14R to reduce the discharge amount. This is to prevent the absorbed horsepower of the main pump 14 as a product of the discharge pressure and the discharge amount from exceeding the output horsepower of the engine 11 .

The arm operation lever 26A is an example of the operation device 26 , and is used to operate the arm 5 . The arm operation lever 26A uses hydraulic oil discharged from the pilot pump 15 to introduce a control pressure according to the lever operation amount to the pilot ports of the control valves 176L and 176R. Specifically, when the arm operation lever 26A is operated in the dark closing direction, hydraulic oil is introduced into the right pilot port of the control valve 176L, and hydraulic oil is introduced into the left pilot port of the control valve 176R. make it When the arm operation lever 26A is operated in the arm opening direction, hydraulic oil is introduced into the left pilot port of the control valve 176L, and hydraulic oil is introduced into the right pilot port of the control valve 176R.

The boom operation lever 26B is an example of the operation device 26 , and is used to operate the boom 4 . The boom operation lever 26B introduces a control pressure according to the lever operation amount to the pilot ports of the control valves 175L and 175R using the hydraulic oil discharged from the pilot pump 15 . Specifically, when the boom operation lever 26B is operated in the boom upward direction, hydraulic oil is introduced into the right pilot port of the control valve 175L, and hydraulic oil is introduced into the left pilot port of the control valve 175R. make it When the boom operation lever 26B is operated in the boom descending direction, hydraulic oil is introduced into the left pilot port of the control valve 175L, and hydraulic oil is introduced into the right pilot port of the control valve 175R.

The discharge pressure sensors 28L and 28R are an example of the discharge pressure sensor 28 , and detect the discharge pressures of the main pumps 14L and 14R, and output the detected values to the controller 30 .

The operation pressure sensors 29A and 29B are an example of the operation pressure sensor 29, and the operation contents of the operator with respect to the arm operation lever 26A and the boom operation lever 26B are detected in the form of pressure, and the detected value is output to the controller 30 . The operation contents are, for example, a lever operation direction, a lever operation amount (lever operation angle), and the like.

The left and right traveling levers (or pedals), the bucket operation lever, and the swing operation lever (all not shown) respectively operate the lower traveling body 1 , open/close the bucket 6 , and turn the upper swing body 3 , respectively. It is a device for operating These operating devices, similarly to the arm operating lever 26A and the boom operating lever 26B, use the hydraulic oil discharged by the pilot pump 15 to set the control pressure according to the lever operation amount (or the pedal operation amount) of the hydraulic actuator. It is introduced into any one of the pilot ports on the left and right of the corresponding control valve. The operation contents of the operator with respect to each of these operation devices are detected in the form of pressure by the corresponding operation pressure sensors, similarly to the operation pressure sensors 29A and 29B, and the detected values are outputted to the controller 30 . .

The controller 30 receives the outputs of the operating pressure sensors 29A, 29B, etc., and outputs a control command to the regulators 13L and 13R as necessary to change the discharge amounts of the main pumps 14L and 14R. . Further, a current command is output to the proportional valves 31L1, 31L2, 31R1, and 31R2 as needed, and the opening areas of the bleed valves 177L and 177R and the negative control throttles 18L and 18R are changed.

The proportional valves 31L1 and 31R1 adjust the secondary pressure introduced from the pilot pump 15 to the pilot ports of the bleed valves 177L and 177R according to the current command output by the controller 30 . The proportional valves 31L2 and 31R2 adjust the secondary pressure introduced from the pilot pump 15 to the negative control throttles 18L and 18R according to the current command output by the controller 30 . The proportional valves 31L1, 31L2, 31R1, and 31R2 correspond to the proportional valve 31 in FIG. 2 .

The proportional valve 31L1 can adjust the secondary pressure so that the bleed valve 177L can be stopped at any position between the first valve position and the second valve position. The proportional valve 31R1 can adjust the secondary pressure so that the bleed valve 177R can be stopped at any position between the first valve position and the second valve position.

The proportional valve 31L2 can adjust the secondary pressure so that the opening area of the negative control throttle 18L can be adjusted. The proportional valve 31R2 can adjust the secondary pressure so that the opening area of the negative control throttle 18R can be adjusted.

Next, the negative control control employed in the hydraulic circuit of FIG. 3 will be described.

In the pipelines 42L and 42R, negative control throttles 18L and 18R are disposed between the hydraulic oil tank and each of the bleed valves 177L and 177R at the most downstream. The flow of hydraulic oil passing through the bleed valves 177L and 177R and reaching the hydraulic oil tank is limited by the negative control throttles 18L and 18R. Then, the negative control throttles 18L and 18R generate a control pressure (hereinafter referred to as "negative control pressure") for controlling the regulators 13L and 13R. The negative control pressure sensors 19L and 19R are sensors for detecting the negative control pressure, and output the detected value to the controller 30 .

In the present embodiment, the negative control throttles 18L and 18R are variable throttles whose opening area changes according to the secondary pressure of the proportional valves 31L2 and 31R2. The opening area of the negative control throttles 18L and 18R decreases as the secondary pressure of the proportional valves 31L2 and 31R2 increases, for example. However, the negative control throttles 18L and 18R may be fixed throttles.

The controller 30 controls the discharge amounts of the main pumps 14L and 14R by adjusting the swash plate inclination angles of the main pumps 14L and 14R according to the negative control pressure. Hereinafter, the relationship between the negative control pressure and the discharge amounts of the main pumps 14L and 14R is referred to as "negative control characteristic". The negative control characteristic may be stored, for example, in a ROM or the like as a reference table, or may be expressed by a predetermined calculation formula. The controller 30 refers to, for example, a table showing predetermined negative control characteristics, and decreases the discharge amounts of the main pumps 14L and 14R as the negative control pressure increases, and decreases the discharge amount of the main pumps 14L and 14R as the negative control pressure decreases. 14R) is increased.

Specifically, as shown in FIG. 3 , when the hydraulic actuators are not being operated in a standby state, the hydraulic oil discharged by the main pumps 14L and 14R passes through the bleed valves 177L and 177R to the negative control throttle ( 18L, 18R) is reached. The flow of hydraulic oil passing through the bleed valves 177L and 177R increases the negative control pressure generated upstream of the negative control throttles 18L and 18R. As a result, the controller 30 reduces the discharge amount of the main pumps 14L and 14R to a predetermined allowable minimum discharge amount, and reduces the pressure loss (pumping loss) when the discharged hydraulic oil passes through the pipelines 42L and 42R. restrain This predetermined allowable minimum discharge amount in the standby state is an example of the bleed flow rate, and is hereinafter referred to as "standby flow rate".

On the other hand, when any one of the hydraulic actuators is operated, the hydraulic oil discharged by the main pumps 14L and 14R passes through the control valve corresponding to the hydraulic actuator to be operated and flows into the hydraulic actuator to be operated. Therefore, the bleed flow rate passing through the bleed valves 177L and 177R and reaching the negative control throttles 18L and 18R decreases, and the negative control pressure generated upstream of the negative control throttles 18L and 18R decreases. As a result, the controller 30 increases the discharge amounts of the main pumps 14L and 14R, supplies sufficient hydraulic oil to the hydraulic actuator to be operated, and ensures the operation of the hydraulic actuator to be operated. However, hereinafter, the flow rate of hydraulic oil flowing into the hydraulic actuator is referred to as "actuator flow rate". In this case, the flow rate of the hydraulic oil discharged by the main pumps 14L and 14R corresponds to the sum of the actuator flow rate and the bleed flow rate.

With the above configuration, the hydraulic circuit of Fig. 3 can reliably supply necessary and sufficient hydraulic oil from the main pumps 14L and 14R to the hydraulic actuator to be actuated when the hydraulic actuator is operated. Moreover, in the standby state, unnecessary consumption of hydraulic energy can be suppressed. This is because the bleed flow rate can be reduced to the standby flow rate.

However, in the hydraulic circuit of Fig. 3, even in the standby state, hydraulic oil corresponding to the standby flow rate is always supplied to the negative control throttles 18L and 18R. In addition, when the hydraulic actuator is being operated, a certain amount of hydraulic oil is always supplied to the negative control throttles 18L and 18R as a bleed flow rate. This is to create a negative control pressure. In addition, this is to allow the discharge amount to be changed quickly according to the movement of the hydraulic actuator.

The smaller the bleed flow rate, the greater the effect of suppressing unnecessary consumption of hydraulic energy. However, the flow rate of the hydraulic oil flowing through the hydraulic actuator tends to fluctuate. In this case, when a pressure fluctuation occurs in the vibration system of the hydraulic system, if the flow rate fluctuation is large with respect to the pressure fluctuation, the vibration becomes large. This is due to the fact that the damping term of the secondary vibration system is expressed by -∂Q/∂P. However, P represents the discharge pressure of the main pump 14 (load pressure of the hydraulic actuator), and Q represents the flow rate of hydraulic oil flowing into the hydraulic actuator. Therefore, when the pressure fluctuation increases with the increase of the load, it is preferable to increase the bleed flow rate in order to reduce the flow rate fluctuation of the hydraulic oil flowing into the hydraulic actuator. Therefore, it is not appropriate to reduce the bleed flow rate uniformly.

Accordingly, the bleed valve control unit 300 of the controller 30 changes the bleed flow rate according to the magnitude of the pressure pulsation, thereby achieving both suppression of unnecessary consumption of hydraulic energy and suppression of pressure pulsation.

The bleed valve control unit 300 controls the opening area of the bleed valve 177 according to, for example, the magnitude of a pulsation in the pressure of the hydraulic oil discharged by the main pump 14 . The opening area of the bleed valve 177 may be controlled according to the magnitude of the pressure pulsation of the hydraulic oil in the hydraulic actuator during operation, such as boom rod pressure, boom bottom pressure, arm rod pressure, and arm bottom pressure. The bleed valve control unit 300 increases the opening area of the bleed valve 177, for example, as the pulsation increases. This is to suppress pulsation by increasing the bleed flow rate (including the standby flow rate in the standby state) and increasing the damping property of the pulsation. On the other hand, the bleed valve control unit 300, the smaller the pulsation, the smaller the opening area of the bleed valve (177). This is to reduce the amount of unnecessarily wasted hydraulic oil by reducing the bleed flow rate (including the standby flow rate in the standby state).

The bleed valve control unit 300 may calculate the magnitude of the pulsation based on the information about the pulsation acquired by the information acquisition device. The information on the pulsation includes boom angle α, arm angle β, bucket angle γ, boom rod pressure, boom bottom pressure, arm rod pressure, arm bottom pressure, bucket rod pressure, bucket bottom pressure, an image captured by the camera S6, and at least one of the discharge pressure of the main pump 14 and the operating pressure of the operating device 26 . The information acquisition device includes the boom angle sensor (S1), the arm angle sensor (S2), the bucket angle sensor (S3), the aircraft inclination sensor (S4), the turning angular velocity sensor (S5), the camera (S6), the boom rod pressure sensor ( S7R), boom bottom pressure sensor (S7B), arm load pressure sensor (S8R), arm bottom pressure sensor (S8B), bucket load pressure sensor (S9R), bucket bottom pressure sensor (S9B), discharge pressure sensor (28), and at least one of the operating pressure sensor 29 and the like. The bleed valve control unit 300 may determine the magnitude of the pulsation in a plurality of stages. In this case, the bleed valve control unit 300 determines, for example, the magnitude of the pulsation in three stages of “large”, “medium”, and “small” based on the output of the discharge pressure sensor 28 . Specifically, when the fluctuation range of the pump discharge pressure in a predetermined time is equal to or greater than the first threshold value, it is determined as "large", and when the fluctuation range is less than the first threshold value and equal to or greater than the second threshold value, it is judged as "medium". is determined, and when the fluctuation range is less than the second threshold, it is determined as "small".

Then, the bleed valve control unit 300 increases or decreases the opening area of the bleed valve 177 by, for example, outputting a control command corresponding to the magnitude of the pulsation to the proportional valve 31 . The bleed valve control unit 300 increases the opening area of the bleed valve 177 by, for example, reducing the current command to the proportional valve 31 and reducing the secondary pressure of the proportional valve 31 as the pulsation increases. . to suppress pulsation. Conversely, as the pulsation is smaller, the current command to the proportional valve 31 is increased and the secondary pressure of the proportional valve 31 is increased, thereby reducing the opening area of the bleed valve 177 . This is to suppress the amount of hydraulic oil that is wasted unnecessarily.

Further, the bleed valve control unit 300 changes the negative control characteristic according to the increase or decrease of the opening area of the bleed valve 177 . In the present embodiment, the bleed valve control unit 300 changes the negative control characteristics by increasing or decreasing the opening areas of the negative control throttles 18L and 18R in accordance with the increase or decrease of the opening area of the bleed valve 177 . This is to prevent the relationship between the lever operation amount and the actuator flow rate from changing even when the bleed flow rate is increased or decreased.

For example, the bleed valve control unit 300 shifts the negative control characteristic to the negative control setting side when the pulsation is high, and shifts the negative control characteristic to the negative control setting side when the pulsation is low, as the pulsation is small, as the pulsation is large.

Compared with the negative control setting in the case of low pulsation, the standby flow rate is higher in the negative control setting for high pulsation, and the rate of decrease of the discharge amount with respect to the increase of the negative control pressure is gentle. That is, if the negative control pressure is the same, the discharge amount of the main pump 14 in the negative control setting at the time of high pulsation is larger than the discharge amount in the negative control setting at the time of low pulsation. Further, when the same discharge amount is realized, the negative control pressure in the negative control setting at the time of high pulsation is higher than the negative control pressure in the negative control setting at the time of low pulsation. However, the actuator flow rate is the same irrespective of the difference in negative control characteristics as long as other conditions including the lever operation amount are the same. For example, if other conditions including the boom raising operation amount are the same, the flow rate of the hydraulic oil flowing into the bottom side oil chamber of the boom cylinder 7 is the same regardless of the difference in the bleed flow rate and the difference in the negative control characteristics. .

In this way, the bleed valve control unit 300 calculates the magnitude of the pulsation and outputs a control command corresponding to the magnitude of the pulsation to the proportional valve 31 . The proportional valve 31 operates the bleed valve 177 to increase or decrease the bleed flow rate. With this configuration, when the pulsation is large, the controller 30 can suppress the pulsation by increasing the bleed flow rate. Moreover, when the pulsation is small, the amount of unnecessarily wasted hydraulic oil can be suppressed by reducing the bleed flow rate.

In addition, in FIG. 3, each of the control valves 171, 173, 175L, and 176L which controls the flow of hydraulic oil toward the hydraulic actuator from the main pump 14L is mutually parallel between the main pump 14L and the hydraulic oil tank. is connected to However, each of the control valves 171, 173, 175L, and 176L may be connected in series between the main pump 14L and the hydraulic oil tank. In this case, even if the spool constituting each control valve is switched to a certain valve position, the conduit 42L is not blocked by the spool, and hydraulic oil can be supplied to the adjacent control valve disposed on the downstream side.

Similarly, each of the control valves 172, 174, 175R, and 176R for controlling the flow of hydraulic oil from the main pump 14R to the hydraulic actuator is connected in parallel with each other between the main pump 14R and the hydraulic oil tank. . However, each of the control valves 172, 174, 175R, and 176R may be connected in series between the main pump 14R and the hydraulic oil tank. In this case, even if the spool constituting each control valve is switched to a certain valve position, the pipe line 42R is not blocked by the spool, and hydraulic oil can be supplied to the adjacent control valve disposed on the downstream side.

Next, a process in which the bleed valve control unit 300 increases or decreases the bleed flow rate (hereinafter, referred to as "bleed flow rate increase/decrease process") will be described with reference to FIGS. 4 and 5 . 4 is a flowchart of an example of the bleed flow rate increase/decrease process. The bleed valve control unit 300 repeatedly executes this process at a predetermined control cycle during operation of the shovel. Fig. 5 shows the temporal transition of the pump discharge pressure and the proportional valve characteristic when the bleed flow rate increase/decrease process is executed during the boom raising operation. The proportional valve characteristic means the relationship between the operating pressure of the boom operation lever 26B and the target secondary pressure of the proportional valve 31 . The proportional valve characteristic may be stored in a ROM or the like as a reference table, for example, similarly to the negative control characteristic, or may be expressed by a predetermined calculation formula. In the examples of Figs. 4 and 5, the proportional valve characteristic is selected from two of the proportional valve setting at the time of high pulsation and the setting of the proportional valve at the time of low pulsation. The target secondary pressure of the proportional valve 31 in the proportional valve setting at high pulsation is higher than the target secondary pressure of the proportional valve 31 in the proportional valve setting at low pulsation when the operating pressure of the boom operation lever 26B is the same. low. That is, when the operating pressure of the boom operation lever 26B is the same, the opening area of the bleed valve 177 in the proportional valve setting during high pulsation is greater than the opening area of the bleed valve 177 in the proportional valve setting at low pulsation. Big. In addition, the opening area of the negative control throttle in the proportional valve setting at high pulsation is larger than the opening area of the negative control throttle in the proportional valve setting at low pulsation when the operating pressure of the boom operation lever 26B is the same.

First, the bleed valve control unit 300 determines whether or not the pressure pulsation in the hydraulic oil flowing through the hydraulic circuit is large (step ST1). In the example of FIG. 4 , the bleed valve control unit 300 determines, based on the output of the discharge pressure sensor 28L, whether the fluctuation range of the discharge pressure of the main pump 14L in a predetermined time is greater than a predetermined threshold value. judge And when it is determined that the fluctuation range is larger than the predetermined threshold, it is determined that the pressure pulsation in the hydraulic oil flowing through the pipe line 42L is large. The same applies to the pressure pulsation in the hydraulic oil flowing through the pipeline 42R. Although the following description relates to the pressure pulsation in the hydraulic oil flowing through the conduit 42L, the same applies to the pressure pulsation in the hydraulic oil flowing through the conduit 42R.

When it is determined that the pressure pulsation is large (YES in step ST1), the bleed valve control unit 300 selects the proportional valve setting at high pulsation as the proportional valve characteristic of the proportional valves 31L1 and 31L2, and high as the negative control characteristic. Select the negative control setting for pulsation (step ST2). In the example of FIG. 5 , the bleed valve control unit 300 determines that the pressure pulsation is large at time t1 and time t3, respectively, and selects the proportional valve setting at high pulsation as the proportional valve characteristic of the proportional valves 31L1 and 31L2. Also, select the negative control setting for high pulsation as a negative control characteristic.

On the other hand, when it is determined that the pressure pulsation is not large (NO in step ST1), the bleed valve control unit 300 selects the proportional valve setting at low pulsation as the proportional valve characteristic of the proportional valves 31L1 and 31L2, and also negative control Select the negative control setting for low pulsation as a characteristic (step ST3). In the example of FIG. 5 , the bleed valve control unit 300 determines that the pressure pulsation is not large at time t2, and selects the proportional valve setting at low pulsation as the proportional valve characteristic of the proportional valves 31L1 and 31L2, and also negative Select the negative control setting for low pulsation as a control characteristic.

Thereafter, the bleed valve control unit 300 determines the target secondary pressures of the proportional valves 31L1 and 31L2 based on the selected proportional valve setting (step ST4). In the example of FIG. 4 , the bleed valve control unit 300 determines the target secondary pressure according to the operating pressure output by the operating pressure sensor 29B with reference to the table related to the proportional valve setting. That is, the target secondary pressure differs depending on the shovel state such as the magnitude of the pulsation at that time, the contents of operation, and the like. In addition, the respective opening areas of the bleed valve 177L and the negative control throttle 18L are uniformly determined according to their secondary pressures.

Thereafter, the bleed valve control unit 300 outputs a current command corresponding to the target secondary pressure to the proportional valves 31L1 and 31L2 (step ST5). The proportional valves 31L1 and 31L2, for example, when receiving a current command corresponding to the target secondary pressure determined by referring to the table regarding proportional valve setting during high pulsation, the bleed valve 177L and the negative control throttle 18L Reduces the secondary pressure acting on each pilot port to the target secondary pressure. Therefore, the respective opening areas of the bleed valve 177L and the negative control throttle 18L increase, the bleed flow rate increases, the responsiveness of the negative control pressure increases, and the damping property of the pressure pulsation increases. As a result, it is possible to attenuate the pulsation of the boom bottom pressure during the boom raising operation. In the example of FIG. 5, the hydraulic oil discharged by the main pump 14, that is, the bottom side of the boom cylinder 7, when the proportional valve setting is selected for high pulsation in the period from time t1 to time t2 and in the period after time t3 It shows that the pressure pulsation of the hydraulic oil flowing into the oil chamber is attenuated. At this time, the bleed valve control unit 300 determines the target discharge amount of the main pump 14L corresponding to the current negative control pressure with reference to the table of negative control settings during high pulsation, and a control command corresponding to the target discharge amount is output to the regulator 13L. The main pump 14L is controlled by the regulator 13L so as to realize its target discharge amount.

Alternatively, when the proportional valves 31L1 and 31L2 receive a current command corresponding to the target secondary pressure determined by referring to the table related to the proportional valve setting during low pulsation, for example, the bleed valve 177L and the negative control throttle ( 18L), the secondary pressure acting on each pilot port is increased to the target secondary pressure. Therefore, the respective opening areas of the bleed valve 177L and the negative control throttle 18L decrease, and the bleed flow rate decreases. As a result, unnecessary consumption of hydraulic energy during boom raising operation can be suppressed. The example of FIG. 5 shows a mode that the proportional valve setting at the time of low pulsation is selected in the period before time t1 and in the period from time t2 to time t3. At this time, the bleed valve control unit 300 determines the target discharge amount of the main pump 14L corresponding to the current negative control pressure with reference to the table of negative control settings during low pulsation, and a control command corresponding to the target discharge amount is output to the regulator 13L. The main pump 14L is controlled by the regulator 13L so as to realize its target discharge amount.

With this configuration, the bleed valve control unit 300 controls the target secondary pressure of the proportional valve 31 when the pressure pulsation is large and the target 2 of the proportional valve 31 when the pressure pulsation is small, even if the operating pressure is the same. Differential pressure can be varied. That is, the bleed flow rate when the pressure pulsation is large and the bleed flow rate when the pressure pulsation is small can be different. Therefore, when the pressure pulsation is large, the bleed flow rate can be increased to attenuate the pressure pulsation, and when the pressure pulsation is small, the bleed flow rate can be reduced to suppress unnecessary consumption of hydraulic energy.

In the example shown in FIGS. 4 and 5, the bleed valve control unit 300 determines whether the pressure pulsation is large based on the detection values of the discharge pressure sensors 28L and 28R for detecting the discharge pressures of the main pumps 14L and 14R. to judge However, the bleed valve control unit 300 includes a boom rod pressure sensor (S7R), a boom bottom pressure sensor (S7B), an arm rod pressure sensor (S8R), an arm bottom pressure sensor (S8B), a bucket load pressure sensor (S9R), Whether or not the pressure pulsation is large may be determined based on a detected value of a pressure sensor that detects the pressure of the hydraulic oil in the hydraulic circuit, such as the bucket bottom pressure sensor S9B.

Next, with reference to FIG. 6, another example of the bleed flow rate increase/decrease process is demonstrated. 6 is a flowchart showing another example of the bleed flow rate increase/decrease process. The bleed valve control unit 300 repeatedly executes this process at a predetermined control cycle during operation of the shovel.

First, the bleed valve control unit 300 calculates the magnitude of the pressure pulsation in the hydraulic oil flowing through the hydraulic circuit as the pulsation degree (step ST11). In the example of FIG. 6 , the bleed valve control unit 300 determines, based on the output of the discharge pressure sensor 28L, the fluctuation range of the discharge pressure of the main pump 14L for a predetermined period of time, the hydraulic oil flowing through the conduit 42L. It is calculated as the pulsation degree indicating the magnitude of the pressure pulsation in The same applies to the pressure pulsation in the hydraulic oil flowing through the pipeline 42R. Although the following description relates to the pressure pulsation in the hydraulic oil flowing through the conduit 42L, the same applies to the pressure pulsation in the hydraulic oil flowing through the conduit 42R.

Thereafter, the bleed valve control unit 300 determines the target secondary pressures of the proportional valves 31L1 and 31L2 according to the degree of pulsation and the operating pressure (step ST12). In the example of FIG. 6 , the bleed valve control unit 300 determines the target secondary pressure according to the calculated pulsation degree and the operating pressure output from the operating pressure sensor 29B.

Thereafter, the bleed valve control unit 300 outputs a current command corresponding to the target secondary pressure to the proportional valves 31L1 and 31L2 (step ST13). The proportional valves 31L1 and 31L2 adjust the secondary pressures acting on the respective pilot ports of the bleed valve 177L and the negative control throttle 18L to their target secondary pressures. Therefore, when the respective opening areas of the bleed valve 177L and the negative control throttle 18L are increased, the responsiveness of the negative control pressure can be improved, and the damping of the pressure pulsation can be improved. As a result, it is possible to attenuate the pulsation of the boom bottom pressure during the boom raising operation. Conversely, when the respective opening areas of the bleed valve 177L and the negative control throttle 18L are reduced, unnecessary consumption of hydraulic energy can be suppressed.

With this configuration, the bleed valve control unit 300 may determine the target secondary pressure of the proportional valves 31L1 and 31L2 in a stepless (seamless) manner according to the magnitude of the pressure pulsation. Therefore, as the pressure pulsation is large, the bleed flow rate can be increased to attenuate the pressure pulsation, and as the pressure pulsation is small, the bleed flow rate can be reduced and unnecessary consumption of hydraulic energy can be suppressed.

As described above, in the shovel according to the embodiment of the present invention, the bleed valve 177 for controlling the bleed flow rate and the bleed valve 177 according to the magnitude of the pulsation in the pressure of the hydraulic oil discharged by the main pump 14 are provided. and a controller 30 for controlling the opening area of the . Therefore, when the pulsation is large, the damping property of the pressure pulsation can be improved by increasing the opening area of the bleed valve 177 to increase the bleed flow rate. As a result, the pulsation of the pressure of the hydraulic oil flowing through the hydraulic circuit can be suppressed. In addition, when the pulsation is small, by reducing the opening area of the bleed valve 177 to reduce the bleed flow rate, unnecessary consumption of hydraulic energy can be suppressed.

As mentioned above, preferable embodiment of this invention was demonstrated in detail. However, the present invention is not limited to the above-described embodiment. Various modifications, substitutions, etc. may be applied to the above-described embodiment without departing from the scope of the present invention. In addition, the features described separately can be combined as long as technical contradictions do not arise.

For example, in the above-described embodiment, the negative control throttles 18L and 18R are variable throttles whose opening area changes according to the secondary pressure of the proportional valves 31L2 and 31R2. And, the negative control throttle 18L, 18R is comprised so that the opening area may become small as the secondary pressure of proportional valve 31L2, 31R2 increases, for example. However, the negative control throttle 18L, 18R may be a fixed throttle as shown in FIG. In this case, the proportional valves 31L2 and 31R2 may be omitted.

In the example of Fig. 7, when the opening area of the bleed valves 177L and 177R increases and the bleed flow rate reaching the negative control throttles 18L and 18R increases, the negative control throttles 18L and 18R, which are fixed throttles, generate The resulting negative control pressure increases. Therefore, the bleed valve control unit 300 controls the movement of the regulators 13L and 13R instead of increasing or decreasing the opening areas of the negative control throttles 18L and 18R according to the increase or decrease of the opening area of the bleed valve 177. By adjusting, that is, by adjusting the swash plate inclination angle of the main pumps 14L and 14R, the negative control characteristic is changed. This is to prevent the relationship between the lever operation amount and the actuator flow rate from changing even when the bleed flow rate is increased or decreased.

With this configuration, the shovel on which the hydraulic circuit shown in Fig. 7 is mounted can realize the same effects as those realized by the shovel on which the hydraulic circuit shown in Fig. 3 is mounted.

Moreover, in the above-mentioned embodiment, each of the control valves 171, 173, 175L, and 176L which controls the flow of the hydraulic oil which goes from the main pump 14L to the hydraulic actuator is via the pipe line 42L, The main pump 14L ) and the hydraulic oil tank are connected in parallel to each other. However, each of the control valves 171, 173, 175L, and 176L may be connected in series between the main pump 14L and the hydraulic oil tank. For example, the control valves 171 , 173 , 175L and 176L may be connected in series via the first center bypass pipe line. In this case, the hydraulic oil flowing through the first center bypass pipe is not shut off by the spool even if the spool constituting each control valve is switched to any valve position. Therefore, even if the spool constituting each control valve is switched to a certain valve position, the hydraulic oil flowing through the first center bypass pipe can reach the adjacent control valve disposed on the downstream side.

Similarly, each of the control valves 172, 174, 175R, and 176R may be connected in series between the main pump 14R and the hydraulic oil tank. For example, the control valves 172, 174, 175R, and 176R may be connected in series via the 2nd center bypass pipe line. In this case, the hydraulic oil flowing through the second center bypass pipe is not shut off by the spool even if the spool constituting each control valve is switched to any valve position. Therefore, even if the spool constituting each control valve is switched to a certain valve position, the hydraulic oil flowing through the second center bypass pipe can reach the adjacent control valve disposed on the downstream side.

With this configuration, the shovel on which the hydraulic circuit is mounted can realize the same effects as those realized by the shovel on which the hydraulic circuit shown in Figs. 3 and 7 is mounted.

This application claims priority based on Japanese Patent Application No. 2017-046770 for which it applied on March 10, 2017, The entire content of this Japanese patent application is used for this application by reference.

One… undercarriage
1A… Hydraulic motor for left driving
1B… Hydraulic motor for right driving
2… turning mechanism
2A… hydraulic motor for turning
3… upper slewing body
4… boom
5… cancer
6… bucket
7… boom cylinder
8… dark cylinder
9… bucket cylinder
10… cabin
11… engine
13, 13L, 13R… regulator
14, 14L, 14R… main pump
15… pilot pump
17… control valve
18L, 18R… negative control throttle
19L, 19R… negative control pressure sensor
26… manipulator
26A… arm control lever
26B… boom control lever
28, 28L, 28R… discharge pressure sensor
29, 29A, 29B... operating pressure sensor
30… controller
31, 31L1, 31L2, 31R1, 31R2... proportional valve
42L, 42R… pipeline
171~174, 175L, 175R, 176L, 176R… control valve
177, 177L, 177R… bleed valve
300… Bleed valve control unit
S1… boom angle sensor
S2… rock angle sensor
S3… Bucket angle sensor
S4… Air inclination sensor
S5… turning angular velocity sensor
S6… camera
S7B… boom bottom pressure sensor
S7R… boom rod pressure sensor
S8B… Arm bottom pressure sensor
S8R… Arm load pressure sensor
S9B… Bucket bottom pressure sensor
S9R… Bucket load pressure sensor

Claims (14)

the undercarriage and
an upper revolving body rotatably mounted on the lower traveling body;
a hydraulic pump mounted on the upper revolving body;
a hydraulic actuator driven by hydraulic oil discharged by the hydraulic pump;
a bleed valve for controlling the flow rate of hydraulic oil flowing in the hydraulic oil tank without passing through the hydraulic actuator among the hydraulic oil discharged by the hydraulic pump;
an information acquisition device for acquiring information on pulsations in the pressure of hydraulic oil supplied from the hydraulic pump to the hydraulic actuator;
and a control device for controlling the opening area of the bleed valve according to the magnitude of the pulsation calculated based on the information acquired by the information acquisition device. The method according to claim 1,
The control device, the smaller the pulsation, the smaller the opening area of the bleed valve, the shovel. the undercarriage and
an upper revolving body rotatably mounted on the lower traveling body;
a hydraulic pump mounted on the upper revolving body;
a hydraulic actuator driven by hydraulic oil discharged by the hydraulic pump;
a throttle for controlling the flow rate of hydraulic oil flowing in the hydraulic oil tank without passing through the hydraulic actuator among the hydraulic oil discharged by the hydraulic pump;
an information acquisition device for acquiring information on pulsations in the pressure of hydraulic oil supplied from the hydraulic pump to the hydraulic actuator;
and a control device for controlling the opening area of the throttle according to the magnitude of the pulsation calculated based on the information acquired by the information acquisition device. 4. The method according to claim 3,
and the control device makes an opening area of the throttle smaller as the pulsation becomes smaller. 4. The method according to claim 1 or 3,
Each of the control valves for controlling the flow of hydraulic oil from the hydraulic pump to the hydraulic actuator is connected in parallel with each other between the hydraulic pump and the hydraulic oil tank. 4. The method according to claim 1 or 3,
and a pressure sensor for detecting the pressure of the hydraulic oil discharged by the hydraulic pump,
wherein the control device detects a magnitude of a pulsation in the pressure of the hydraulic oil based on a detected value of the pressure sensor. 4. The method according to claim 1 or 3,
a pressure sensor for detecting the pressure of hydraulic oil in the hydraulic actuator;
wherein the control device detects a magnitude of a pulsation in the pressure of the hydraulic oil based on a detected value of the pressure sensor. 4. The method according to claim 1 or 3,
A shovel that determines the magnitude of the pulsation in a plurality of steps. 4. The method according to claim 1 or 3,
A shovel for changing a relationship between a control pressure for controlling a regulator and a discharge amount of the main pump in response to an increase or decrease in the opening area. The method according to claim 1,
A shovel, wherein a fixed throttle is disposed downstream of the bleed valve. 4. The method according to claim 1 or 3,
and a control valve for controlling hydraulic oil for the hydraulic actuator,
The shovel, wherein the main pump and the hydraulic oil tank are not blocked by the spool due to a change in the position of the spool constituting the control valve. The method according to claim 1,
The pulsation is a fluctuation range of the hydraulic oil pressure. 4. The method according to claim 1 or 3,
A shovel, wherein a relationship between a lever operation amount and a flow rate of hydraulic oil flowing through the hydraulic actuator does not change even when the opening area is changed. the undercarriage and
an upper revolving body rotatably mounted on the lower traveling body;
a hydraulic pump mounted on the upper revolving body;
a hydraulic actuator driven by hydraulic oil discharged by the hydraulic pump;
a throttle for controlling the flow rate of hydraulic oil flowing in the hydraulic oil tank without passing through the hydraulic actuator among the hydraulic oil discharged by the hydraulic pump;
a control device for controlling the opening area of the throttle according to the magnitude of pulsation in the pressure of the hydraulic oil supplied from the hydraulic pump to the hydraulic actuator;
A shovel for changing a relationship between a control pressure for controlling a regulator and a discharge amount of the main pump in response to an increase or decrease in the opening area.

Images